I. Field of the Invention
The present invention relates to an electromagnetic coupler.
II. Description of Related Art
In its application to a vehicle, an electromagnetic coupler can be used for example to transmit mechanical power between an internal combustion engine and the wheels of the vehicle, by adjusting at will and continuously the torque and the speed on the latter. It can also be used, where appropriate, to provide a motive or generative electromechanical energy conversion in conjunction with electrical energy storage means. It can therefore be particularly useful in transmissions or hybrid electrical traction systems of motor vehicles.
As shown in FIG. 1, an electromagnetic coupler 10 conventionally comprises:                an input shaft 12 intended to be mechanically coupled to a motive source,        an output shaft 14 intended to be mechanically coupled to at least one element to be driven,        a casing 16,        and two electrical machines.        
The first electrical machine M1 comprises in this illustration:                an input rotor 20, having an axis A, driven rotation-wise by the input shaft 12 and comprising a first armature 22 and        a crown 23 of inner magnets 24 magnetically coupled with the first armature 22 and borne by an output rotor 30 of axis A mounted to rotate on the casing 16 and in a mechanical drive relationship with the output shaft 14.        
The first armature 22 has windings 52 installed in its magnetic circuit 60, and electrically connected to an electrical power source, conventionally one or more batteries 32, via a first electronic unit 34.
Conventionally, the first electronic unit 34 is modeled to transform the direct current output from the battery 32 into a polyphase current, the phases of which feed the windings of the first armature 22, and vice versa. The windings of the first armature 22 are distributed in a known manner around the periphery of the input rotor 20 so that the polyphase current circulating there can generate a first rotating electromagnetic field.
The first electronic unit 34 is driven by a driver unit 36 designed to allow for control of the “slip”, that is, the difference between the rotation speeds of the input rotor 20 and the output rotor 30, in particular by modifying the frequency of the electric current. Depending on whether the slip is positive or negative, the first armature 22 can be generator or receiver, that is, the transfer of energy between the output shaft 14 and the battery 32 is in the direction of a charge or a discharge of that battery, respectively. This additive or subtractive transfer of energy is reflected in a variation of the rotation speed of the output shaft 14.
In synchronism, that is, at zero slip speed, the input 12 and output 14 shafts are linked as they would be by a direct mechanical coupling, the first armature 22 then receiving only the electrical power needed for magnetization, that is, a direct current.
The second electric machine M2 comprises:                a second machine stator 40, fixed to the casing 16 and bearing a second armature 42 comprising a plurality of coils 100 installed in its magnetic circuit 43, and        a crown 44 of outer magnets 45 of the output rotor 30 with which the second armature 42 is magnetically coupled.        
The coils of the second armature 42 are fed with polyphase current via a second electronic unit 46 connected to the battery 32 so as to generate a second rotating electromagnetic field.
The driver unit 36 controls the second electronic unit 46 to control the additive or subtractive torque introduced by the machine M2 on the rotor 30 and therefore the output shaft 14.
Conventionally, the magnets of the crowns 23 and 44 can, for example, be replaced by an asynchronous squirrel cage, or even by teeth with reluctance, the design of the first and second corresponding armatures being adapted accordingly.
Conventionally, the driver unit 36 controls the electronic units 34 and 46 according to angular position information concerning the input 20 and output 30 rotors, and settings typically supplied by the driver of the vehicle.
The position information can be supplied by position encoders, not shown, or deduced from other measurements.
The two electric machines can cooperate so that the electrical power derived from the slip of the first machine is used by the second electric machine to produce an additional mechanical torque on the shaft 14.
Patent AU 5840173 describes various embodiments of electromagnetic couplers.
By acting on both electric machines, it will be understood that it is thus possible to adapt the transmission speed- and torque-wise at will and, where appropriate, exploit the potential of an electric energy storage.
The electrical energy supply for the first armature 22 conventionally requires sliding electric contacts 48 between the first fixed electronic unit 34 and the rotating windings of the first armature 22. The sliding contacts 48 represent a topological integration constraint, volume-wise, in terms of compatibility with the physical environment and reliability. They also constitute a not inconsiderable cost center.
To avoid such sliding contacts, U.S. Pat. No. 6,380,653 discloses an electromagnetic coupler in which the first armature 22 comprises a first machine stator, or “first stator 50” having an axis A, that is fixed, and bearing coils 52 (see FIG. 2) and an input rotor 20 without windings, made of a cylindrical support provided with peripheral ferromagnetic studs. The stator 50, fixed to the casing 16, is concentric to the input rotor 20 and radially separated from the latter by an additional air gap 54. The coils 52 of the first armature 22 are conventionally introduced into longitudinal peripheral notches, that is, notches extending along the axis A, provided on the surface of the first stator 50, according to the normal method of producing polyphase machine armatures.
The coupler disclosed in U.S. Pat. No. 6,380,653 does, however, have a large footprint. Furthermore, its operation generates high Joule losses.